fast primes.
unless you're loaded with money, or you're always shooting in bright conditions, then that's really you're only choice. sports moves fast, and you're going to need quite fast shutter speeds to be able to keep up (at least above 1/500th) without getting motion blur. I'd suggest against the 70-300 IS, which might be good for general stuff (i've heard it's much sharper than the older 75-300 IS), but is definitely not a lens that is designed for sports. It's slow, and since the players move quickly, you'll need quick shutter speeds, and the IS might help a little bit, but mosly just with panning. Also, it runs for around 650 USD...you can get much nicer, faster lenses for that price. How close can you get to the action? If you are able to get pretty close (right on the sides) you wont need as long of a lens, so I'd suggest the 85 1.8 (around 350 USD) for that. It's an absolutely terrific lens. If you cant get that close, I'd go for the 200mm 2.8L or the 300mm f4L IS (the 200 you can get for like 600 USD i believe, and the 300 for about 1100 USD - sorry i know you dont buy with USD but i dont know alot of prices the other way around...). The 70-200 2.8L is a great one like darich said, and you can 'zoom right in' with that one, and it's much faster...but also much more expensive. you can get the sigma version (which is also quite good) for much less, as well as canon's older 80-200 2.8L (terrific lens also, but doesnt focus very fast - which you need for sports). keep in mind that the 350d has a faster focusing mechanism that kicks in with apertures of 2.8 and larger (numerically lower). hope that helps some!